It is known in the art to install a performance amplifier within a vehicle, such as an automobile, in order to modify audio frequency signals generated by the vehicle's sound system. With such known amplifiers, audiophiles can continue listening to high-fidelity sound reproductions of music and speech, even while traveling in their automobiles. These amplifiers are conventionally mounted in the trunk or under one of the front seats of the automobile.
Conventional amplifiers adapted for installation in a vehicle may have external adjustment controls so that a listener can fine tune, for example, the audio frequency response of the amplifier to suit his desires, the acoustic environment in the vehicle, and/or any deficiencies in equipment or recordings. These external controls extend through a face of the amplifier's housing and are electrically connected to the main circuitry of the amplifier, but do not change the basic operating characteristics of the amplifier. That is, a listener can only modulate the audio signals within the basic operating characteristics of the amplifier and cannot achieve a totally different sound unless a new amplifier with different operating characteristics is installed.
While amplifier arrangements employing externally mounted components for establishing operating characteristics of an amplifier are known, the applicant is not aware of such an arrangement being adapted for use in a vehicle. U.S. Pat. No. 3,466,564 to Weischedel discloses an amplifier unit having the above construction. However, such amplifier units are inoperable without an external circuit board being connected thereto. Further, such external arrangements are not practical when units are to be mounted within an open area in a vehicle which may be moving thereby exposing the external circuitry to shifting articles.
In order to improve the aesthetics of known external link-up units, plug-in circuitry units have been developed, for example, in the measuring equipment field which house the circuitry components in a single unit and can slide into a recess in the main housing of the device. Such equipment includes a common housing which can receive one of a plurality of function modules. A multifunction device of this type is described in U.S. Pat. No. 3,619,776 to Kinninger. U.S. Pat. No. 4,131,851 to Martiny et al. discloses a radio signal receiver with plug-in modules. However, both these instruments are incomplete without a module unit which determines the function of the instrument.
In particular, the receiver of Martiny et al. includes a housing with a sealed recess in which a plug-in module must be inserted to link the various circuitry stages of the receiver in the proper sequence to produce a coherent receiver. A variable power amplifier for musical instruments having an opening in its housing for receiving a plurality of pluggable signal processing modules is described in U.S. Pat. No. 4,644,289 to Kennedy et al. However, at least two pluggable signal processing modules need to be inserted into one of several electric terminals to electrically connect first and second electrical signal processing channels of the amplifier's circuitry.
Further, a protective cover which closes the opening through which two of Kennedy's modules are inserted is removed when the device is in use. Accordingly, the electrical circuitry of Kennedy's power amplifier is exposed once mounted for use and is not practical since the electric circuitry is not protected from dust, etc. Thus, with conventional amplifier arrangements, a consumer must purchase the required plug-in units to complete the circuitry of the basic amplifier and still may have problems due to circuitry damage (requiring further expense) since the modules units are not built into the device.
While the above-described conventional plug-in module units may overcome aesthetic disadvantages associated with externally mounted circuitry modules, the circuitry (if any) within the main housing of the device does not produce an operable device. As a result, several functional disadvantages are associated with these known devices in that the additional modifying circuitry is produced as a part of the basic amplifier circuitry, but is an external unit to the basic amplifier. Thus, a consumer is required to purchase an expensive device which is not operable along with separate, external units which determine its function. Further, these external circuits are not securely held within the device and thus can be damage subjecting a consumer to more expense just to operate his basic amplifier.
Therefore, it can be seen that there is a need for an amplifier unit having basic operating characteristics which can be inexpensively modified by a consumer to create a different amplifier unit and has a sturdy cover for protecting its circuitry.